1. Field of the Invention
The present invention relates to a semiconductor device and a method for manufacturing the semiconductor device.
2. Related Background Art
Patent Literature 1 (Japanese Unexamined Patent Application Publication No. 05-291621) discloses an ohmic contact to a c-plane of a layer using a metal such as Ag or Ni on GaxAl1-xN doped with a p-type impurity. After the deposition of a metal layer, annealing is performed in an oxygen atmosphere. A high intensity light-emitting device having a low driving voltage is thereby produced using a gallium nitride-based semiconductor.
Patent Literature 2 (Japanese Unexamined Patent Application Publication No. 09-64337) discloses an ohmic contact of a c-plane to a p-type layer. A nickel layer is formed on a surface of p+ layer, and a gold layer is formed on the nickel layer. Subsequently, through heat treatment, the distribution of the elements in depth direction is inverted. As a result, nickel and gold are distributed in that order from the surface.
Patent Literature 3 (Japanese Unexamined Patent Application Publication No. 11-186605) discloses an electrode formed on a p-type GaN contact layer. After a light-transmissive electrode is formed on a Mg-doped GaN contact layer 17, treatment of low resistivity of a p-type and alloying of the electrode are concurrently performed through annealing in a gas containing at least oxygen at a temperature of 500° C. to 600° C.
According to a method disclosed in Patent Literature 4 (Japanese Unexamined Patent Application Publication No. 2004-247323), an AlN buffer layer is formed on a sapphire substrate, and a GaN layer and a layered body doped with magnesium are formed on the AlN buffer, followed by heating at a temperature of 300° C. After the heating, a metal electrode having a thickness of 50 nm is formed on the layered body by vapor deposition.